The goal of this consortium is to establish tools that can be used as biomarkers and/or sensitive and reliable objective assays of social impairment in autism spectrum disorder (ASD) clinical trials. Specifically, we aim to accelerate the development of effective treatments for social impairment in ASD by validating (a) outcome measures that will be sensitive and reliable assessments of response to treatment and EEG and (b) eye-tracking (ET) biomarkers that can be used to reduce heterogeneity of samples via stratification, indicate early efficacy, and/or demonstrate target engagement. The consortium will conduct a naturalistic, longitudinal study of preschool (3-5 years) and school aged (6-11 years) children with ASD and typical development (TD) with IQ ranging from 50-115. Children will be assessed across three time points (T1: Baseline, T2: 6 weeks, T3: 24 weeks) using clinician, caregiver and lab-based (LB) measures of social impairment, along with a battery of conceptually related EEG and ET tasks and independent ratings of clinical status. This battery measures key facets of social-communication in ASD using well-validated paradigms appropriate for this developmental and cognitive range. Five Collaborating Implementation Sites (Sites), all highly experienced in multi-site collaborative clinical research using the methodologies proposed here in both typical and atypical development, will contribute equally to recruitment, screening, diagnosis, testing, and longitudinal assessment. The Data Coordinating Core (DCC) will provide a secure informatics infrastructure to streamline communication and data flow throughout the consortium to ensure organized, secure data management, quality control, and reliable upload to the National Database for Autism Research and NIH/NIMH Data Repositories. The Data Acquisition and Analysis Core (DAAC) will oversee consistent application of scientific standards and methodological rigor for standardized data collection, processing, and analytics. The Administrative Core will oversee the operations of the Sites, the DCC, and the DAAC to coordinate with federal and private partners in this cooperative agreement to: 1) Compare whether LB measures versus clinician and caregiver assessments of social impairment are more sensitive indicators of clinical status; 2) Evaluate whether this set of ET and EEG measures, individually or in combination, has potential utility as stratification biomarkers and/or sensitive and reliable measures of change in clinical trials, assessing viability in terms of: construct validity; test-retest reliability, consistency, and stability; discriminant validity ; convergent validity; and sensitivity to change; 3) Collect blood (DNA) samples from subjects and parents of ASD subjects for future genomic analyses and share raw, processed, and analyzed data to create a community resource accessible for use by all qualified investigators.